Characterization of Er–Ba nanoparticle suspension-doped aluminosilicate optical fibers for 1550 nm amplification

In recent years, the scalability of erbium-doped fiber (EDF) towards high power (kW) lasing in amplifiers has been constrained, in part, by modern methods which insufficiently improve the solubility of Er³⁺ ions in silicate glass. Without adequately declustering the ions, they are likely to interact non-radiatively with increasing concentration, resulting in lower gain and output power. Finding a new means for improving the solubility of erbium ions in silicate fiber would create opportunities to break decades-old benchmarks in fiber amplifiers and lasers. This work compares six EDFs fabricated via a novel doping method utilizing precursors that contain nanoparticles comprising Ba:Er fluorides. These fluorides oxidize during fiber fabrication, rendering a baria-rich environment in the vicinity of the erbium ions-. Through a combination of both the nanoparticles and alumina contained in the precursor, average erbia densities as high as 2 wt.% are realized. Heavily doped fibers with quantum efficiencies up to 0.76 are demonstrated. Additionally, lasing efficiencies that match and even exceed commercial EDFs with similar or lower ion densities are presented. Whether the baria affects the solubility of the erbium ions and our current understanding of the fiber due to the doping process are discussed.